The present invention relates to video encoders/decoders, particularly, to video encoders/decoders which encode or decode video data according to any video compression/decompression standard.
Data received by a video processing and display system is typically in a compressed format. Advances in compression and decompression techniques coupled with the ability to integrate ever increasing number of transistors on a semiconductor substrate, have led to development of new systems for storage and processing of audio and video data.
Many different video compression and decompression standards currently exit. One widely known standard is JPEG (Joint Photographic Expert Group). In the JPEG standard, to compress video data, the size of the bitmapped images are reduced by discarding some of the pictorial information, though with little discernable image degradation.
Another widely known video compression standard is MPEG1 (Motion Picture Expert Group) which provides improved video quality, as well as random access, fast forward and reverse playback of video data.
A subsequently developed standard known as MPEG2 extends the basic principles of MPEG1 to a wider range of applications. The MPEG2 provides for fully digital transmission of broadcast-quality video at bit rates of 4 to 9 Mega bit per second.
In the DVD standard, which is also a known standard, MPEG2 is used for compression and decompression of video data while MUSICAM and AC-3 are used to compress and decompress audio data. A compressed data bitstream generated in accordance with the DVD standard includes interleaved data substreams, such as video substream, sub-picture unit substreams, and navigation substreams. Each substream consists of data packets having a packet header and a packet payload. The packet header, among other things, identifies the substream to which the packet belongs. The packet header also includes information specifying the payload type and size, as well as one or more compression parameters which may be required for decompression. Typically, audio data packets will be further divided into audio data frames, with each frame having a frame header and a frame payload.
To reconstruct the original data from e.g. the DVD bitstream, a DVD decompressor locates the beginning of a packet, then reads the packet header to determine the substream membership. The decompressor then routes the packet payload and portions of the packet header to the associated elementary bitstream buffer. Subsequently, the decompressor decompresses the contents of each buffer to reconstruct the original sampled data (i.e. audio, video, SPU, navigation), which is finally delivered e.g. to a display monitor and speaker.
A new video compression and decompression standard, MPEG4, has recently been established which provides for very low bit rate (VLBR) encoding of video signals.
Many of the conventional video processing systems contain a number of Integrated Circuits (IC) to decode or encode video data. Furthermore, such systems are standard-specific and, as such, are typically unable to support multiple compression standards.
Moreover, many of the conventional portable battery-operated video processing systems employ a Central Processing Unit (CPU) to decode or encode video data. In such systems, for e.g. each compressed stream of data supplied to the CPU, many CPU operations and thus many clock cycles are required to decompress the data. Therefore, to decode/encode compressed video data in such a systems, the CPU must typically run at relatively high frequencies (e.g. 800 MHz) which thereby shortens the life of the battery powering the system.